The invention relates to an active spring-and-damper system for inserting between a vehicle body and a wheel suspension member comprising a piston/cylinder unit having a pressure chamber for static load support and two additional pressure chambers for dynamic load control. The pressure chambers are arranged in a cylindrical housing and are equipped with connections for hydraulic lines.
The coordination of spring-and-damper systems at the chassis of motor vehicles consists of a compromise between driving safety and driving comfort. In the case of known "passive" spring-and-damper systems, the force between the vehicle body and the wheel is only a function of the spring travel and the damper speed. Energy can only be stored by means of a spring or absorbed by way of a damper. These limitations necessarily result in a considerably restricted range in which driving safety and driving comfort can be coordinated.
Through active interventions into a spring-and-damper system according to DE-OS 27 38 455, a mechanism is provided to shift these range restrictions toward more driving safety and more comfort. By means of this known active spring-and-damper system, an arbitrary force may be applied as a function of various influencing variables. Hydraulic control elements are preferably used for generating the force. A basic static wheel load is supported by means of an integrated conventional hydropneumatic spring element and only the dynamic forces are applied by way of an active control element. According to DE-OS 27 38 455, a known control element of the active spring-and-damper system has effective areas of a different size which therefore generate unequal volume flows in the direction of pull and in the direction of pressure. In addition, a spring strut is equipped with a plurality of dynamic sealing devices for the mutual sealing of the pressure chambers.
It is an object of the invention to provide an improved control element having a shorter overall length and a simplified construction by which approximately equal volume flows are generated between the pressure chambers. Also these pressure chambers are closed off with respect to one another with the smallest possible number of dynamic sealing devices.
According to the invention, this object is achieved by having the first and second pressure chambers in a cylindrical housing and separated by a piston. The piston is connected with a hollow piston rod forming the third pressure chamber, and all pressure chambers are sealed off with respect to one another by means of at least three sealing devices. A coaxially arranged guide rod is connected with the cylindrical housing and extends into the third pressure chamber inside the hollow piston rod and to the housing floor. The piston rod is connected through the housing floor through a sealing device.
Alternatively the first pressure chamber can be provided in the cylindrical housing, a second pressure chamber provided inside a hollow piston rod, and third pressure chamber is arranged in the cylindrical housing, partially surrounded by the first pressure chamber and closed off by means of a guide rod connected with the piston rod. The guide rod projects into the pressure chamber and is guided through the housing floor of the cylindrical housing by a sealing device. Here the first and third pressure chambers are coaxially disposed inside one another and the first pressure chamber has a circular-ring-shaped cross-section and the third pressure chamber has a circular cross-section. The first pressure chamber is formed between a wall of the hollow piston rod and a wall of he cylindrical housing and comprises a first effective surface. The second pressure chamber is arranged inside the shaft of the piston rod and has another effective surface. Here the first pressure chamber is closed off by two circumferential sealing devices and the second and the third Pressure chambers are sealed off by means of additional sealing devices provided in the housing floor.
The principal advantages achieved by the invention are that a cylindrically designed housing in connection with a hollow piston rod, forms three pressure chambers with two cooperating pressure chambers being controllable for the dynamic wheel load and another pressure chamber being used for the support of the static wheel load. The pressure chambers are arranged such that the shortest possible overall length is obtained and are connected to at least three pressure inlets.
The control element consists essentially of two components which are guided in one another to form the pressure chambers between them and are sealed off with respect to one another by means of at least three dynamic sealing devices.
For generating equal volume flows from and into the cooperating pressure chambers during the compression and rebound of the control element, the effective surfaces in these pressure chambers are of approximately the same size.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.